system of tuning keyboard instruments, prevalent from c. 1500 through the 18th century. It enabled keyboard instruments to play in five or six closely related keys, rather than in only one key. The system supposedly used in medieval monophonic (melody-only) music, just intonation, derived the proper tuning of all the intervals in the scale by various additions and subtractions of perfect natural fifths and thirds (in tune with the fifths and thirds found in the natural harmonic series, perceivable as faint overtones above a fundamental note). This process resulted in whole tones of two sizes. When an instrument tuned, say, in C was played in G, the large and small whole tones were in the wrong order, and the instrument sounded sourly out of tune. Meantone tuning substituted a single, mean whole tone, hence its name.
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